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Study: Don't overlook vitamin D for bone health

Your best efforts to bone up on calcium may not be enough to prevent osteoporosis if you aren't getting enough vitamin D, research shows.

A study in the Journal of the American Medical Association looked at the relationship between vitamin D status, calcium intake and levels of parathyroid hormone (PTH), which plays a major role in maintaining calcium levels in the blood, and found that calcium alone was not enough to maintain ideal levels of PTH in cases where vitamin D was lacking.

The study involved 944 Icelandic adults who filled out food questionnaires in order to determine their vitamin D and calcium intakes over the previous three months. Because exposure to sunlight is a major source of vitamin D, subjects were recruited in equal numbers throughout the year in order to account for seasonal differences.

Levels of PTH, calcium and serum 25-hydroxyvitamin D, an indicator of vitamin D status, were measured using a blood test.

After analyzing the data, the researchers found that vitamin D played a bigger role than calcium in regulating levels of PTH, even in cases where calcium intake was below recommended levels.

"Our results suggest that vitamin D sufficiency can ensure ideal serum PTH values even when the calcium intake level is less than 800 mg per day, while high calcium intake (greater than 1200 mg per day) is not sufficient to maintain ideal serum PTH, as long as vitamin D is insufficient," the researchers wrote.

In order to keep bones strong, Osteoporosis Canada recommends 1000 mg of calcium and 400 IUs of vitamin D per day for adults between 19 and 50 and 1500 mg of calcium and 800 IUs of vitamin D per day after the age of 50. But research presented at the 11th World Congress on the Menopause in October found that more than half of postmenopausal women who have osteoporosis are vitamin D deficient.

"These results underscore the need to improve physician and patient awareness of the importance of adequate vitamin D supplementation in postmenopausal women with osteoporosis," the researchers said.

According to the authors of the study, more research still needs to be done to determine what amounts of vitamin D would be most beneficial.

But they add that "there is already sufficient evidence from numerous studies for physicians and general practitioners to emphasize to a much greater extent the importance of vitamin D status and recommend vitamin D supplements for the general public, when sun exposure and dietary sources are insufficient."

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